class_docstr: Python data source backed by Python objects: length and __getitem__.
code: def __len__(self) -> int:
      return self.length
  
file_path: datasets/tensorflow_datasets/core/data_sources/python.py
imports: from __future__ import annotations
  from collections.abc import MappingView, Sequence
  import dataclasses
  from typing import Any, Callable
label_desc: Use image node_id 1 for calling the PythonDataSource obj's underlying member method code with example usage: obj.__len__() and returns: self